Process of and apparatus for treating sulphuric acid containing dissolved nitro bodies



May 9, 1944. F. F. CHAPMAN ETAL 2,343,323

PROCESS OF AND APPARATUS FOR TREATING SULPHURIC ACID CUNTAINING DISSQLVED NITROBODIES Filed Jan. 10, 1941 2 Sheets-Sheet 1 EJECTOE CONDENSER VAPOR SEPARA T0]? 7 ATMOSPHERE 2 ii 1 E W 5 i E F ii 1 l :I I i I :i i i E i i; DEA/N i 34!. 1 I i L 5: g I 1, STEAM DEA/N i i i :5 CONDN8E6AL TANK i 122 s 2 l i i! i u I i a? i i gas a ACID 46/01 I l I a L1, z I AC/D SEAL TANK HEAT/N6 6 FLU/D INVENTORS- Fred-F Cfiza man CZz'fiorciA. 0003521229 Y May I 9, 1944.

F. F. CHAPMAN ETAL PROCESS OF AND APPARATUS FORVIREATING' SULPHURIC ACID CONTAINING DISSOLVED NITROBODIES Filed Jan. 1O,- 1941 Concen/ra/o'r i Cbncen/ra/or 5/0/3 62 aware 2 Sheets-Sheet 2 fiPed FC/za man Cid/ordA. Wc a oduzy BaokFPeZersozz INVENTORS ATTORNEY Paramec m lrnocnss onmnnrrI-Amwsjoa smime; SULPHURIC g acm CONTAINING s-mslFrcd Francis IChapman, :wflmingtonhand "Ralph mneisl'etetson, Bellefonte, DeL, anacuuom Akeley woodbury, Media,;l!a assig'nors to E.;I.

{.du Pont de Ne our's-& Company, Wilmington,

DeL, a corporationof Delaware 7 Application January 10,;19 41,-Serial No. amass Claims.

invention relates to the concentrationand purification of residual acid.

Certain processes known to the prior art, although adequate in other respects, have a proved to be completely imsatisfactory for the removal of aromatic nitrobodies from the residual acid..

Th object of invention is an improved process a for the concentration andfpurification. of sulphuric acid containing organic impurities. such as nitrobodies orthe like particularlythosehof aromatic origin. Afurther'cbiect is an improved apparatus for. concentrating and purifying. said -acid.. Other obiectsivillwbe app rent from the following description of; the invention,

We have found that; the foregoing objects are accomplished whensulphuric .a'cid, containingorganic matters such as nitrobodies from'thelmanufacture of explosives Or the like, iscaused to flow in a condition of f h ghksurface exposure, as jinla thin :layer or "film down over the inner "surface of one or more substantially werticaiexternally heated tubes, under-reduced -1 pressure, and continuously from saidi tubes-I down through :at' least one barometric i leg which is preferably heat-,in-

sulated and not cooled, intota sealitank -and then permitted to flow through eheated wtubes Prefer ;ably inclined upward; and-:nnally flow intoa a 1e- 2 illustrates the processthereof.

The details l of the process and apparatus of the invention may be "more treadily :understood from :the ifollowingydescriptionl of rthepreferred embodiment thereof wherein ,7 reference :is a mad to thevarious parts ofitheflgJ-l.

The residual acidcontainingtnitrobody"isconcentrated j-rapidly ,asxa 51in thewertical tubes il, 7 provided twithv -heatingjiackets 2 :85 r

showlrlin 11.. i concentrated a acid 5 leaves of 'thevertical; tubes :and passesfdownward through'the; barometriclegs Z3 ,1suitably.;con-

:structed of. :Duriron {Ll-hese baromejtric legs; which are preferablyginsulatedrandsare not cooled, dil -into thesea-l-ktankl. gtl'hisiatankglike the leg, also, preferably heatginsulateditofminimlze heatilosses. z Accordingly,athegaciditherein 7 may :haveiit'jtempemturednithe z neighborhoods r 300" I}. .The levelizof ithekacid {5 in the seal i ismaintainedsui'iicientlyihish soztha zthe"baro- 4 i tr'ic'gleg dip ben ath lwthesurfacegoi ithe acid. 555 ephuric acid ,whicln-hasibeen matstreatedaccord- From theseal; tank the hot; acid is. caused to flow by gravity through the upwardly inclined tubes 5. ThesegarepreferablysDuriron tubes provided with jackets listhrough whichhot oil or the like 5 isvcirculated,;D 7eferably ata' temperature from 500552.? F. ,Thisserves to'heatthe acid from about 300 F. to approximatelyABOF, The size 1 of v the tubes is such thatthe time of g'passage of acidrlthrough. themis preferably inthe neighborl0 hood of1.30fminutes, permitting decomposition of ;the nitrobody. The tubes, are inclinedsufljlciently to retainmaifull bodyofacid in: them. However, the exit;.end of 1' these heating =tubes s is keptat a l level" slightly; lower than the toprotthe-seal tank 45 to, prevent the overflow of liquid fromtheilatter.

' The gas .vent 1 .uisrprovided atithe upper-end. of

the purification tube. 'Ihe;aci fromithesehating tubesi flows; into the-retention ;8. of such size as to} provide qa-{furthervretention 'offlthe"hot 20 acid for approximately L451minutes longer, in

order to permit 1 dccompositionsandlor carboniz- .aticn :of :the -nitrobody to fvgo substantially to completion. ,jA ccordinsly, retention tank is heat+insulated 1 and 7 may beaconstructed of brick 'andleadi-lined-steel. {The:acidwithmitrobddy destroyed then leavestheretentionatank through itube 19,; passes; through 1 the Qcooler i I land ist-sent out -at i l I eto storage; or J to g further conventionaiusage. sometimesrithisacid is'treatedwith a0 1 oxidizing agents tooxidize :the-rcarbonwto carbon Q dioxide. Nitriotacid may h usedtorltni -purpose g-Qther elements inithe; concentrating -apparatus lwhichiare shown ,-ini the drawingst and1described bylegendare-the;condenser,xtheivaporseparator,

:135 and; the distributor. w'Ihese areconventional elements and need nozexplanation.

The gfore'going{descriptionconstitutes 1 the preferred embodiment .of :our invention ,.-;How ever,

we; do; not dritend-gtosbe limitedalthereby. 1,For1.in- ;40 ..stance,=s,whi1eithelpurifying apparatus and; process is especially advantageous when employed with 5 the. falling film-:ltypeIQficoncentrator; as, described, :it is nevertheless applicable also ztotany; conven- .-t-iona1ityp,e. oficonce'ntrating;apparatus onprocess,

:45 sbutrparticularly those,processesvwherein theiacid isconcentrated under lvacuum,--:or-';by; passing-ihot ,gases through ithe :acid, especially; in the L1 event that the atmospheric boiling :point mi the :acid is:not:reached.

ne ihishly advantageous adaptation of :the -;present 1 invention may ,be understood "thy grater. ring' to-3the ;flow, :sheet.:shownf insFigure I Liwherein; a process gisidescribed for-1 concentratinginitric lacidiby means :ofitheaiconcentrtfld trresiduali sul.

ing to our invention, to destroy the nitrobody therein. The residualacid from the manufacture of trinitrotoluene, diniti'otoluene, or the like, is passed through a conventional denitrating means to recover the nitric acid therefrom, leaving what is known as dark residual acid containing a relatively high content of organic mat-,

ter. This dark residual acid is passed through i a sulphuric acid concentrating unit, for instance such as that described in the foregoing. The concentrated acid is heat-treated to effect iurther decomposition of organic matter. The resulting acid is a dark sulphuric acid having a concentration cf approximately 92%. This dark con-' centrated acid-is then mixed'with weak nitric acid to form a concentrating mix. This concentrating mix is passed through a nitric acid concentrating' unit from which strong'nitric acid is 1. The process of treating the residual sulphuric acid containing nitrobodies. or the like, which comprises passing said acid continuously in the form of a thin layer down and over the inner surface of a heated substantially vertical tube, and down through a heat-insulated barometric leg at the'base oi? said tube into a heatinsulated seal tank, thereby maintaining said acid in said tank at approximately 300 F., flowsaid acid from the region of the base of said seal tank upwardly through inclined tubes-heating. the acid in said tubes from approximately 300 F. to approximately 480 F., the time of recovered 1 The sulphuricacid issuing from the uhitjis light in com-.- substantially free mm genie-matter," and has a strength of approximately '70-'73'%-su1phuric acid. It is then otsatisfactory quality for use in other processes where dark acid of high organic content would be objectidnable; Forinstance itmay be sent to the light residual acidstorage in a system wherein. a battery of sulphuricacid concentrators is used in conjunction with a battery of nitric acid concentrators for thelproduction of strong nitric;

acid;

Although we preferto employ the heat-treating unit'illustrated in Figure I for the purpose set forth in Figure -II,'-it should be understood that it is an advance in the art to employ any heat-treatingunit in such a process.

The process of the present invention is par-:

ticularly advantageous in that it accomplishes satisfactorily the removal of nitrobodies which are aromatic'in nature; These nitrobodies have not been removed successfully by certain'pro'ce esse'softhe'prior art. It may-be that-the success of the present process in the removal of the same is .due to the fact that nitrobodies ofthis type are particularly stable" at high temp-p peratures and require prolonged heating: at 1evated temperatures to bring about theirdecomposition.

The method and'apparatus ofthis in vention are particularly advantageous for plantssengaged in the manufacture ofmunitions and otherexplosives, wherein the concentration :efiresidual sulphuricacid is complicated by .tlieiipresence of dissolved nitrobody orbther organic-matesmt n- I 'Although we prefer tovoperate withathe purl 'flcation tube inclined upwards, as described in the foregoing, it be understood that this tube may 'be in any other suitable position. 'If'or' .instaricegit' may be arranged horizontally with a dammirfgmeans or some similar arrangement for obtaining the prolonged heating described.

passageof said acid through said inclined tubes being approximately 30 minutes, flowing said acid into a heat-insulated retention tank and retaining the acid in said tank for approximately 45 minutes, to produce a concentrated sulphuric acid free from nitrobodies. i

2. An apparatus for-the concentration and purification of residual sulphuric acid containing dissolved nitrobodies or the like, which comprises in series, a condenser, a vapor separator, a distributor, at leastone vertical heated falling film tube, at least one barometric leg at the foot.

ing dissolved nitrobodies-or the like,.comprising an acid concentrating unit provided with means for maintaining a reduced pressure therein, and connected with said unit, a heat-insulated barometric leg dipping into a heat-insulated seal tank,anv upwardly inclined purification'tube provided wtih heating means, and a heat-insulated retentiontank arranged to receive the flow of acid from the upper end of said purification tube, said apparatus elements being connected in sequence permitting gravity flow. s

4. The process of treating residual sulphuric acid containing nitrobodies or the like, which comprises passing. said acid continuously in the form of a thin layer down and over the inner surface of a heated substantially vertical tube and down through a barometric leg at the base of said tube intoa seal tank, flowing the same We intend to be limited only by the following a V patent claims.

'We claim:

-from nitrobodies.

through a heated tube and into a retention tank, at such rate and temperature that said acid is retained at a temperature from approximately 3003.15. to 480 F. for approximately'75 minutes to produce ,a concentrated sulphuric acid free man FRANCISYCHAPMAN. RALPH FRANCISPETERSON. crn'r'onn a. WOODBURY. 

